Abatement efficiencies of organic matter and micropollutants during combined coagulation and powdered activated carbon processes as an alternative primary wastewater treatment option

Abstract

A combined process of coagulation and powdered activated carbon (PAC) was tested as an alternative primary wastewater treatment option to remove dissolved organic matter and organic micropollutants (OMPs). Bench-scale experiments were performed using three coagulants (Al2(SO4)3, PACl, and FeCl3) and four PAC materials (SPC, F400, BL, and SPO). The removal of dissolved organic carbon (DOC) and 43 selected OMPs were determined after treating wastewater influent with separate and combined (sequential and simultaneous) processes involving coagulation and PAC. For all coagulant types, coagulation alone at a coagulant dose of 20 mg (Al or Fe)/L achieved a satisfactory removal for DOC (35–36%); however, the removal efficiencies of OMPs were low (mostly<5%). Adsorption alone at a PAC dosage of 75 mg/L (specific dosage: 4.3 mgPAC/mgDOC) effectively removed DOC (37–48%) and most OMPs (63–99%); however, the removal efficiencies were low for metformin and perfluorinated compounds (<40%). Among the four PAC materials, SPO showed the best removal performance for DOC and OMPs, which could be attributed to the greater abundance of mesopores (5–10 nm). The sequential and simultaneous application of coagulation (20 mg (Al or Fe)/L) and PAC (120 mg/L) led to the higher removals of DOC (57–61%) and most OMPs (53–99%) compared to coagulation and adsorption alone, indicating that the coagulation and adsorption did not interfere with each other. Considering the advantages of a longer contact time and smaller reactor footprint, simultaneous dosing of PAC to a coagulation reactor is advantageous over sequential dosing. Our results are useful for designing and optimizing the chemically enhanced primary wastewater treatment.